One method of recycling used rubber products is to grind it into fine scrap and work it into new rubber as an elastomeric filler. Reclaiming rubber from rubber articles usually entails devulcanising said articles and rendering the devulcanised material mouldable and revulcanisable into new articles. One of the earliest non-chemical devulcanisation methods is the "heater process" patented by Hiram L. Hall in 1858 which comprises subjecting lightly vulcanised used rubber products (boots and shoes) to steam heat so that the used rubber can be successfully devulcanised by the heat at a temperature higher than 150.degree. C. and for a period longer than the original vulcanisation.
Later, chemical processes were used in devulcanising the sulphur crosslinks, including the use of mixtures of compounds including conventional accelerators as in U.S. Pat. No. 4,211,676 (Bridgestone) and EP-A-0,690,091 (Sekhar).
However, in all these chemical reclaiming processes, the initial stage is physically reducing the size of scrap rubber, usually by grinding used rubber materials to obtain the scrap. This is most generally accomplished using corrugated two-roll cracker mills or a rotating cutter to obtain a rip, tear or shear action, while others have rotating-knife slitter actions (Schaefer and Isringhaus, "Reclaimed Rubber", Rubber Technology, 3rd ed.).
The rubber crumbs obtained from the initial milling stage may be crumbed or lumped together to form blocks using oils and petroleum-based products and used as filler materials or in the aforementioned chemical processes for reclaiming rubber. Such conventional physical methods normally use rubber scraps obtained from used rubber products that have high tensile strength (due to their high content of carbon black and lower rubber content of about 40%) such as vehicle tires.
Highly elastic used rubber products such as surgical gloves and inner tubes of tires which have higher rubber content (about 70%) are more difficult to cut due to its elasticity and therefore not normally used as raw materials in reclaiming process. The conventional processes avoid such high rubber content products since it would be difficult to physically cut such elastic scraps and devulcanise enough of the sulphur crosslinks to enable effective revulcanisation and reclamation.